It may become necessary to detect the presence position of a metal substance in a determined area, particularly in a plane area, for example, to detect a move path of a metal substance moving in a plane area or when metal substances distribute in one area, to detect their distribution pattern. A specific example of the former is to detect a move path of game play media in a gaming machine.
With some gaming machines, a player moves a metal substance, such as a metal ball, in a specific space set in the gaming machine and may or may not win the play depending on the destination of the metal ball. Pinball machines are typical of such gaming machines; with a pinball machine, a player plays a game by dropping a metal ball called a "pinball" in a space sandwiched between parallel planes in which a large number of obstacles are located.
A general pinball machine has a base board for providing a space required to move pinballs, a glass plate spaced from the base board at a given interval to cover the base board, and a propelling mechanism for propelling pinballs in the space provided by the base board and the glass plate. The pinball machine is set up so that the base board becomes substantially parallel to the vertical direction. The base board is formed with a plurality of safe holes for the player to enter a pinball in for a winning game play through which the pinball is discharged from the base board and an out hole into which pinballs not entered in the safe holes are finally collected for discharging the pinballs from the base board.
A large number of pins (nails) are set up substantially vertical to the base board in a state in which they project from the base board as long as the diameter of a pinball as obstacles with which pinballs dropping along the base board frequently collide for causing their motion direction to fluctuate. The pins are located on the base board as a distribution determined so as to guide pinballs colliding with the pins toward or away from the safe holes while causing the motion directions of the pinballs to fluctuate.
By the way, winning game play conditions at each pinball machine need to be managed at pinball parlors having a large number of such pinball machines. That is, personnel of the pinball parlor need to find machines having an unbalanced or abnormal path of pinballs for replacing or repairing them. For example, if machines which are easy for players to win game plays are left as they are, the pinball parlor suffers a great administration loss; such machines need to be found. In contrast, if the pinball parlor contains machines which are abnormally hard for players to win game plays, the pinball parlor will lose their customers; such machines need to be found. Also, while players play games, personnel of the pinball parlor need to find some players performing such illegal operation as guiding pinballs with a magnet, etc.
A conventional metal substance detection system for such purposes is described in Japanese Patent Laid-Open No.Hei 2-279186.
In the gazette, a pinball detection system is disclosed. The detection system has a metal sensor called a sensing matrix comprising a transmission coil row group in which transmission coil strings with continuous transmission units like open rings are arranged in one direction and a reception coil group in which reception coil strings with continuous reception units like open rings inductively coupling with the transmission units are arranged in a direction crossing the transmission coil row group. The metal sensor is connected to a controller for sensing whether or not a metal substance exists in each overlap of the transmission and reception units.
The metal sensor can be attached to a glass plate covering a base board of a pinball machine for detecting the presence position of a pinball on the base board of the pinball machine.
By the way, a large number of transmission and reception coil strings need to be installed to raise the detection accuracy. However, they comprise coils like open rings, thus have a complicated structure, and the wiring density cannot be raised.
In contrast, the present applicant proposed a sensor comprising transmission lines and reception lines in place of coil strings in the specification of the application in Japan (Japanese Patent Application No. Hei 2-244898, Japanese Patent Laid-Open No. Hei 4-122375, laid open to public inspection on Apr. 22, 1992: which was open after the priority date of the present application and not prior document for the present application), wherein the sensing matrix comprises a plurality of parallel turned transmission lines installed on one face of a wiring board and a plurality of parallel turned reception lines installed on the opposed face of the wiring board crossing the transmission lines so that the reception lines are electro-magnetically coupled with the transmission lines. The transmission lines and reception lines of the sensing matrix are connected to a transmission circuit and reception circuit of the controller, a signal current is made to flow into the transmission lines in sequence, and current induced by the signal current is taken out for each reception line in sequence, whereby the presence or absence of a metal substance is detected from the induced current detected at the reception circuit and the position of the metal substance can be detected from a combination of the transmission line on which the signal current flows and the reception lines on which the reduced current is received.
By the Way, when such a metal substance detection system has a wide detection area and requires accuracy, it comprises a large number of transmission and reception lines. Thus, when detecting a metal substance, the detection system scans each of a large number of transmission and reception lines and it takes time to detect the metal substance. Particularly, when the target changes as it moves as in gaming machines, position accuracy will be degraded if the target is not detected quickly.